1. Field of the Invention
The present invention relates to hydrogen storage containers for accommodating hydrogen absorbing alloys, and more particularly to hydrogen storage containers adapted for stabilized supply of hydrogen gas from a hydrogen absorbing alloy accommodated therein.
2. Background Art
Developed in recent years are devices, such as fuel cells, hydrogen motor vehicles and heat pumps, wherein the energy source is hydrogen gas. Hydrogen gas is supplied to these devices utilizing a hydrogen absorbing alloy which reversibly absorbs or desorbs hydrogen. The alloy is accommodated in the form of a powder or molded body in a specified container.
To give an increased hydrogen storage capacity to the container, it is desired that a larger quantity of hydrogen absorbing alloy be accommodated in the container. Instead of filling the container with the alloy in the form of a powders therefore, the alloy is often accommodated in the container in the form of a molded body which is prepared from a mixture of alloy powder and a binder (e.g., PTFE) by compression molding and the subsequent sintering or like treatment and which is externally shaped in conformity with the interior configuration of the container.
For example, FIG. 26 shows a hydrogen storage container 90 for containing molded bodies 91 of hydrogen absorbing alloy. The container 90 comprises a tubular body 92 closed at one end, open at the other end and having a circular cross section, and a lid 93 closing the opening. The molded bodies 91 are placed into the container through the opening and accommodated therein as stacked up. After the molded bodies 91 have been accommodated, the opening is closed with the lid 93 attached to the tubular body 92, for example, with fastening members 94 such as bolts and nuts or by welding. The lid 93 has joined thereto piping 95 for releasing hydrogen gas, causing the container 90 to communicate with a fuel cell or like device therethrough.
With hydrogen storage containers, it is desirable that the hydrogen gas desorbed from the alloy be supplied to the device with good stability.
The hydrogen absorbing alloy becomes more finely divided with the absorption and desorption of hydrogen gas to exhibit a reduced hydrogen absorbing-desorbing capacity. Accordingly, there arises a need to replace the alloy within the container to ensure the desired hydrogen absorbing-desorbing capacity. With the container described, however, it is necessary for the replacement of the alloy to take out the alloy from the container by removing the tubular body from the lid and turning the body upside down, hence the drawback of requiring a time-consuming procedure. It is therefore practice to remove the piping from the device and replace the alloy as contained in the container.
The hydrogen absorbing alloy desorbs hydrogen gas through an endothermic reaction, so that the temperature of the alloy drops with the desorption of hydrogen gas, gradually decreasing the amount of hydrogen gas to be desorbed. In order to cause the alloy to desorb a sufficient amount of hydrogen gas with good stability, it is accordingly necessary to heat the alloy to some extent and preclude the drop in the temperature.
A container is available which is internally provided with heat transfer fins for heat exchange and thereby adapted to control the temperature of the alloy to overcome the problem of temperature reduction (see, for example, JP-B-36081/1992). As shown in FIG. 27, a device is also available which comprises a heat medium tube 96 inserted in a container 90 through a wall thereof, and an external heat source 98 operable by electricity, gas or other external energy source for heating a heat medium to pass the heated medium through the tube 96 and raise the temperature of a hydrogen absorbing alloy. Nevertheless, since the fuel cell, hydrogen motor vehicle or the like utilizing hydrogen gas as its energy source is used generally at a location where an external power source, gas or other energy source is not readily available, it is difficult to heat the alloy by the external heat source.
Additionally, when internally provided with the heat transfer fins or the heat medium tube 96 as stated above, the container 90 can be packed with a powder 97 of hydrogen absorbing alloy, but encounters difficulty in accommodating a molded body of hydrogen absorbing alloy, therefore has the drawback of a reduced hydrogen storage capacity and is further likely to rupture owing to the swelling of the alloy due to the absorption and desorption of hydrogen.